Derby Talk

Derby Talk is a forum for Pinewood Derby, Awana Grand Prix, Kub Kar Rally, Shape N Race Derby, Space Derby, Raingutter Regatta and other similar races where a child and an adult work together to create a race vehicle and a lot of fun and memories

So I am working on my last cub car (like to get mine done before my son starts on his). I wanted to make a very simple car to show off the car materials-namely the pine and tungston. Yet I kept thinking it would be fun to really take advantage of the rule not requiring all 4 wheels to touch the ground and came up with a second design. I figured I would likely break one so might as well work on both. So here the are. The question is which one to I race? Pine or Orange? Or do I figure out which is fastest and race that one?
Noskills

Vitamin K wrote: I kind of like the Pine one, with the "Tungsten Reveal."

Seth, I like the cars! ... But if I had to vote on which car right now!

I sure would like to see.. if I could get Stan,
To talk about about the Equilibrium Equation of flow through Gaps.
(such as the gaps seen between the tungsten cubes )

Because I can't seem to recall.. If it's the flow that's proportional to the velocity at each gap.
Or if it's the.. Velocity that is assumed to be proportional to the square root of pressure difference
between the gap.

Vitamin K wrote: I kind of like the Pine one, with the "Tungsten Reveal."

Seth, I like the cars! ... But if I had to vote on which car right now!

I sure would like to see.. if I could get Stan,
To talk about about the Equilibrium Equation of flow through Gaps.
(such as the gaps seen between the tungsten cubes )

Because I can't seem to recall.. If it's the flow that's proportional to the velocity at each gap.
Or if it's the.. Velocity that is assumed to be proportional to the square root of pressure difference
between the gap.

Nice looking cars Seth.. Stick to the car you like the best.

Whoda.

Hi Seth,

Those two are real beauties and I have a difficult time picking one.

The clear coat is the more towards my style of build with a "truth in materials".

However...

The wheel on top is very cool, and I like the paint job and and aero details around the "raised" wheel... But the way that you handled the front axle holes on it pushes it over the top.

My vote is the red car.
Nice work!
Joe

Whoda,
It is difficult to tell if you were joking or not because that sounds so Stan.
And I must admit that it made me curious to hear his thoughts on the subject.
Best,
Joe

Thanks for the input all. I think I will race the orange one at the pack meeting for the "wow" factor and the pine one at the districts (just because I want too )
If given the chance I will try to see which is faster. May have some adult competition at the pack level this year-damned Boeing engineers!
Noskill

Laserman wrote:
Whoda,
It is difficult to tell if you were joking or not because that sounds so Stan.
And I must admit that it made me curious to hear his thoughts on the subject.
Best,
Joe

Joe, I was not joking around!
Seth, has two different car shapes here and he is asking which car to race.

Some like his orange car with the fender & wheel on the top of it..
and some like how the tungsten cubes are showing on the next car.

The orange car looks to be set up to ride on 3 wheels.. if so how much weight is on the DFW?

The Tungsten cube car has lot of weight (24 cubes) in the back.. but what about the weight on the DFW?
Will the air flow through the gaps of the tungsten cubs affect how the rear wheels track.
& maybe cause a death rattle or so just by the air flow.

So I was looking at how the air would flow over and around the two different cars.

Then the Equilibrium Equation of flow through gaps struck a nerve that I was trying to recall
how it worked. I'm thinking I'm way off.. with the flow through gaps equilibrium equation.

Noskills wrote:Thanks for the input all. I think I will race the orange one at the pack meeting for the "wow" factor and the pine one at the districts (just because I want too )
If given the chance I will try to see which is faster. May have some adult competition at the pack level this year-damned Boeing engineers!
Noskill

It sounds like the best of both worlds Seth!

I was kind of assuming that you would fill the gaps between the cubes with clear tape or something to avoid drag.

While we are on the topic though...

I once postulated to a buddy that aero drag on top of the car is more severe than the drag below the body.

At the time I was figuring that the drag on the car would be further from the track and so it would have a greater lever arm to amplify the drag.

My buddy told me that was crazy.

Hold on! I see what you mean now Whoda.

He is asking which car we think would win given all things being equal.

I like the red one if the rules allow. The wheel way over in the middle shifts a bunch of weight off the raised wheel.

Also... The natural wood one should have those gaps filled.

I like to use acetate that goes into a printer. I use double sided vinyl tape around the edges of the gap, cut the acetate with scissors and paste it down.

Then I can sand it to make sure it is smooth and not bumby.

Top and bottom on those holes for the wood one and I think it will help with aero.

It doesn't have to be that double sided vinyl tape, I bet that Super Spray 77 or even elmers white glue could work the same way (if used sparingly).

Joe,
I plan to cover the pine car top and bottom with clear packing tape. The spaces between the cubes are tiny and filled with epoxy. Will post speed results on both cars. Kids are are coming along. Will have some nice photos soon. Made a two tone snake patter than I really like!
Noskills

Noskills wrote: Will have some nice photos soon. Made a two tone snake patter than I really like!

"O" Boy! I can't wait to see a photo of snake car.. hope it looks real enough to make me run.. out the room.
Hope I did not pick on you to hard about the gaps seen in the tungsten cubes Seth..
As i was just looking at the ( air flow) of the 2 cars seen.